Method for producing pulp from printed unselected waste paper

ABSTRACT

A waste paper recycling process relates to the treatment of a mixture of waste paper containing non-cellulosic contraries and printing inks, in order to release the contraries from the fibers and further to separate them from the stock in order to produce re-usable pulp for the production of paper and board. 
     The invention has to do with new and useful improvements in methods for first removing the non-ink contraries from the fibrous mass and second releasing and then removing the ink particles from the said fibrous mass. 
     The invention is directed to the treatment of the fiber slurry produced during the ink separation stage, after the ink releasing stage has been applied. One aim of the process is to allow both the use of the fibers and the mineral fillers contained in that slurry, for pulp and board making, and the use the solids-free water contained in the same slurry as the washing liquid in the previous ink-separation treatment, thus closing the fibers and the water circuits. 
     This process includes chemical and thermo-mechanical treatments, starting under alkaline conditions, which may become neutral at the end of the process.

.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of reissue application Ser. No.08/054,951 filed Apr. 27, 1993, entitled METHOD FOR PRODUCING PULP FROMPRINTED UNSELECTED WASTE PAPER, now abandoned, which is a continuationof reissue application Ser. No. 07/600,012, filed Oct. 18, 1990, nowabandoned, which is an application for reissue of U.S. Pat. No.4,780,179 issued Oct. 25, 1988, which .Iaddend..[.This.]. is acontinuation of co-pending application Ser. No. 482,623 filed on Apr. 6,1983, now abandoned.

FIELD OF THE INVENTION AND REVIEW OF THE PRIOR ART

Recycling of waste paper is possible only after most of the noncellulosic contaminants have been removed from the fiber mass. Thesecontaminants may have been introduced during the printing steps (carbonblack, pigments, ink vehicles, ink fixating polymers, etc. . . ), duringconverting, (varnishes, coats, binders, wrapping, etc. . . ) and laterduring the collecting phase (metallic pieces, plastics, soils and dirtof any kind).

Removing of the contraries generally occurs based on chronologicaldimensional sequences, through screening, magnetic separation, first indry conditions and later in aqueous suspension.

The fiber mass is then screened through perforated plates and finercontraries are removed by centrifugal and centripetal cleaners.

The ink particles are not substantially removed during the precedingsteps, and this operation is achieved in two steps: (a) detaching theink particles from the fiber surface, through the combined action ofchemicals, temperature and mechanical shear forces and (b) removingthese particles from the pulp slurry.

Generally, all the contraries including the ink particles, are releasedfrom the fibers during the defibering phase. The waste paper is treatedin a pulper, under alkaline conditions at 50°-60° C. temperature, inorder to be well defibered and transformed into a pumpable slurry. Analternative to this process is to operate the pulper in cold conditions,then thicken the pulp above 15% consistency, then heat the pulp withsteam at 60° C. introducing at that point the de-inking and bleachingchemicals. The pulp then remains in a reaction tower during 2-3 hourswithout any mechanical action.

The first drawback of these techniques is that all contaminants aresubmitted to the thermal treatment, including the ones which have lowmelting points, such as binders, hot melts, plastics and other"stickies". By this way, they become dispersed and cannot be removed anymore by the conventional means, and will precipitate again on papermachine elements such as doctor blades, wires, felts, pipe walls, etc. .. , creating operating problems and loss of efficiency.

A second drawback is that these ink-releasing techniques have a weakaction on the modern inks such as the rotooffset inks, where inkvehicles are made of synthetic resins which form an insoluble polymer onthe surface of the fibers. The same consideration applies for xerocopyprinted paper and varnished papers, where temperatures in the range of60° C. will provide neither any softening of the ink vehicles nor anyweakening of the bondings between the fibers and these vehicles.

An other limitation of these techniques is that it is not possible toincrease the temperature of the ink releasing step, because thecombination of the alkalinity and the temperature during a long timewill result in an unacceptable yellowing of the pulp, specially if somegroundwood is present in the mixture to be treated.

Ink removing techniques in use to-day are essentially two: floatationand washing.

In flotation, the diluted fiber slurry is intensively mixed with airafter a hydrophobe ink collector has been added. Then stock is naturallydeaereted and air bubbles collect the ink particles during the upwardstravel to the surface. The resulting black foam is then collected andtreated separately through centrifuges, then disposed of;

In washing, a very old and well known process, the finest dispersedparticles are removed through several dilutions and squeezing cycles,generally arranged as a counter-current cascade configuration. Theeffluent of the first squeezing sequence contains all the free fine inkparticles, but also a great quantity of fine cellulosic fibers and mostof the mineral fillers, and are sewered and treated according to thelocal pollution regulations.

Some other ink removing techniques exist, such as solvent extraction buthave not been followed by wide indutrial application, due to highproduction cost and low quality of the produced pulp.

In the U.S. Pat. No. 4,076,578 Puddington et Al. recall the fundamentalconcept of de-inking: (a) releasing ink from the paper fiber by mean ofchemicothermomechanical treatment and (b) separating of dispersed inkparticles from the pulp, then proposes a different method to achievethis goal, through absorption of the ink particles onto the surface ofsolid particles, followed by the removal of said particles from thepulp, and then removal of the ink from those solids.

Nowadays, none of the above mentioned processes has asserted itselfbecause each of them presents some drawbacks.

The flotation is a low consistency process (between 1% and 2%) and thusinvolves high volumes of pulp, with consequent high investment cost.Also, the nature of this process is essentially physico-chemical andthus its stability is greatly related to the sability of the compositionof the waste paper, the type of fibers (chemical or mechanical), thetype and content of mineral filler, the calcium ion concentration.Consequently, the brightness of the de-inked pulp shows undesired highfluctuations. These brightness variations are also accompanied by allcomposition variations coming together with the raw material (wastepaper), without any possibility of control or continuous measurement andmonitoring.

To-day, it is generally admitted that the first condition for the goodoperation of a modern fast papermachine is the constancy of operatingparameters, the most important one being the composition of the stockfeeding the machine. Unfortunately, it is not possible to control thecomposition of a waste paper lot as easily as a virgin pulp bale. Forthis reason, the efficiency decrease of high-speed paper machines usinghigh percentages of flotation de-inked pulp is mainly caused by theuncontrolled variations of the stock composition rather than by thebrightness (or de-inking efficiency) variations. This problem can besolved using selected classified waste paper, at a price which makes thede-inked pulp uncompetitive respect to the virgin pulp, assuming thatsuch type of waste is available.

Finally, the flotation process needs to be continuously controlled, on athree shift basis, by highly specialized chemical experts usingsophisticated instrumentation and laboratory, thus appreciablyincreasing the production cost.

The washing process involves simpler, cleaner, and easier to controlequipment, in particular when washing occurs at consistencies between 3%and 15%.

This process does not require any specialized control and it is admittedthat not only the quality (cleanliness and strength) of the washed pulpis definitely higher than for the floated pulp, but this quality is muchmore constant and less sensitive to raw material variations ofcomposition, thus offering a higher "runability" of the pulp in thepaper machine room.

In fact, the principle of washing on a perforated plate statisticallysays that elements having a smaller size than the plate openings shouldpass through the plate. It appears that the variations of composition ofthe stock to be de-inked (fines, groundwood, mineral fillers) willreverberate on the fraction lost through the plate, giving a finalproduct almost constant in quality, if not in quantity. This principleallows for the use of unselected waste paper, a lower quality producthaving a much lower cost and higher availability.

On the other hand, this process needs a much higher quantity of water,and produces the equivalent higher quantity of effluents which stillcontain a great quantity of valuable products, cellulosic short fibers,mineral fillers, mixed together with the undesired ink. Besides thatdirect loss, it is necessary to consider the indirect cost due to theabatement of the pollution created by the solids contained in theeffluents.

In conclusion, it can be said that if flotation de-inking presents highinvestment and operating cost together with low constancy of the qualityof the final product, washing de-inking also shows a high similar costof the product due to both the intrinsical low yield of the process andthe pollution abatement cost.

In order to minimize the negative aspects of each one of these basicprocesses, their supporters have proposed several combinations of them,keeping in mind to produce only one de-inked pulp starting from onewaste paper mixture.

In the French patent application No. 79 19392, M. Fritz Zeeb of VoithCy. suggests to remove the fine fibers fraction together with themineral fillers from a flotation de-inked pulp, using screens andstrains arranged as washing elements. This process, which is onlysummarily described without any example, seems to add up both costs anddrawbacks of flotation and washing.

In the TAPPI magazne, vol. 63, No. 9, September 1980, M. Lothar Pfalzerof the same Voith Cy., while recalling the same concept (page 116, FIG.3), specifies that the fine fiber fraction and mineral fillers arecentrifugated and then disposed of and lost. It also appears from thispublication that the effluent is totally sedimented after having beenfloculated by addition of aluminum sulfate, but it is also specifiedthat a good dispersion of the ink particles can be obtained at high andwell controlled pH. These two statements are rather contradictory andmake this concept hardly applicable in practice.

M. Pfalzer also suggests the opposite philosophy (page 114, FIG. 1),which consists of a total flotation followed by a total sedimentation ofthe effluents of a conventional washing process. For the same reasons asabove, which are: the low yield of the washing process, thenon-compatibility between ink dispersing high pH and aluminum sulfatesedimentation low pH, the addition of the costs and drawbacks of eachindividual process, this proposal has not been applied on an industrialscale.

In the French patent application No. 78 29637, M. Calmanti of MontedisonCy. suggests in a more simple way to separate the ink particles from thefine fibers and the mineral fillers contained in the effluents of awashing process, by means of a simplified flotation process where nochemicals are added. It is also stated that the chemicals added at thebegining of the process (pulping stage) will also provide for the inkcollecting function. In this process, the so called "clarified"effluents which actually contain most of the fibers and mineral fillerslost during the washing step, are totally recycled ahead of the process.

A tentative application of this process had to be quickly abandoned fortwo reasons. At first, it has not been possible to obtain a satisfactoryselective removal of the ink during the flotation, because of theantagonistic functions of the two chemicals mixed together at thepulper: (a) dispersing of the ink needed during washing, (b) coagulationof the ink needed during flotation. So, too much fibers and fillers werefloated together with the ink resulting in a quick overloading of thesewer system, and immediate shut down of the plant.

Second, it has not been possible to recirculate continuously ahead ofthe washers, an effluent which contains most of the fines and fillerslost by the same washers. This total recirculation has quickly resultedin (a) a drop of the brightness due to the poor ink removal efficiencyand (b) an unacceptable drop of the hydraulic capacity of the thickeningelements. Both can be attributed to the saturation of the circuit withfines and fillers, dimensions of which are of the same order ofmagnitude than the ink particles.

In the Italian patent application No. 26944 A/80, M. Calmanti recallsthe same principle, where the effluents at a concentration of 0,14%would be selectively floated with the only addition of air, and thentotally recycled ahead of the process together with their suspendedsolids. M. Calmanti nevertheless suggests to install a "quick"flotation, a third flotation, installed ahead of the washing process.This configuration does not seem to bring any answer about the two basicprevious problems; (a) how is it possible to have the best dispersiontogether with the best coagulation, (b) how is it possible to avoid thesaturation, the clogging of the thickening elements, and the loss of theink removal efficiency, due to the recirculation of the fines and thefillers together with the effluent.

GOALS OF THE INVENTION

The present invention aims to provide a practical and integralindustrial process which allows to produce, in a continuous way andstarting from a mixture of unselected waste papers, three separateproducts, namely:

(a) a totally cleaned and de-inked pulp having constant and controlledbrightness and fiber classification, having a very low and constantfillers content;

(b) a totally cleaned and de-inked pulp having a fine fiberclassification and a very high fillers content, these two parametersbeing variable in both quality and quantity;

(c) an effluent which does not practically contain suspended solids,which has not been submitted to any pH reversion, which does not containany floculation or sedimentation chemical agent, and thus is immediatelyand totaly re-usable as the dilution and washing liquid during the inkremoval step of the de-inking phase.

A further aim of this invention is to provide a practical andadvantageous improved method for de-inking these grades of printedpapers and boards which cannot be correctly de-inked by conventionalmethods.

An other aim of this invention is to provide a practical andadvantageous method which allows high quality paper and board at highspeeds using the low quality waste grades which could not be used forsuch noble purpose when treated by conventional methods.

The invention is also directed to the application of modified andpurposely adapted ink removal processes, such as washing, selectiveseparation, flotation, coagulation, filtration, onto the highink-content slurry produced by the primary ink removal process.

The invention also aims to allow for the use in paper making of theby-products of a washing de-inking process, either on the paper machinewhich will use the primary pulp, or on a different paper machine.

An object of this invention is to provide a to create a constant andcontrolled composition of the pulp used for paper making, which can bedifferent from the composition of the incoming waste paper mixture. Thisobject is achieved by pumping controlled flows of each one of the twocomponents and mixing them ahead of the paper machine(s) in the desiredpercentage; the capacities of the chests act as buffers between wastepaper and paper machine stock compositions.

An other object of this invention is to increase the value of theby-product (the secondary pulp) by the fact that good long fibers can beextracted from the main line in order to optimize the operation both ofthe selective separation of the ink and of the filtration on fiber mat.

A further object of this invention is to accomplish the selectiveseparation of the ink at a stage where this ink is highly concentrated(approximately three times more than in the main pulp), thus increasingthe efficiency of the chemicals.

An ulterior object of this invention is to achieve the selectiveseparation of the ink (which is the more delicate operation of the wholerecycling process), in a satellite circuit of reduced capacity(approximately one third of the flow through the main line), thus beingeasier to operate and requiring lower investment cost.

This invention then aims to insure the highest possible constancy ofquality of the primary pulp, by the fact that the variations of finesand fillers contents will instantaneously reverberate on the fractionproduced by the satellite circuit, which in turn can also be stabilizedby mean of a thorough mixing and high retention time in the final bufferchest.

With these and other aims and objects, the nature of which will becomemore apparent, a fuller understanding of this invention will be gainedby reference to the following detailed description and the appendedclaims.

DESCRIPTION OF THE INVENTION

The following detailed description, together with the attached schematicflow-sheet, refers to one preferred practical application of theinvention, although other procedures can also be applied.

Following the flow-sheet, the bales of waste paper (1) are loaded into apulper (2) by means of a loading mechanism, together with the recycledwater and eventual caustics in order to bring the pH at values above 7.It is possible but not mandatory to introduce part or all of thequantity of dispersing chemicals required by the ink-releasing action,during the pulping operation.

The pulp is then diluted using recycled water and pumped through one orseveral stages of screens and cleaners (3) in order to releasecontraries and contaminants from the paper surface, and further removethem from the pulp slurry.

When the de-inked pulp is used for high quality paper production or onhigh-speed machines, such as light weight coating base or newsprint,this operation must be done in the same way it is done with chemical ormechanical virgin pulps, using the same equipment and operatingparameters. In particular, the best results have been obtained through acombination of pressurized slotted screens equipped with 0.3 mm. slotwidth working at 1% consistency followed by 4 inch size cleaners workingat 2,8 bars pressure drop and 0,6% consistency in the first stage.

It is anyhow of paramount importance that the temperature of the stockbe kept as low as possible so that the low melting point contaminantswill remain rigid and will not extrude through the slotted screens andthus be eliminated by the screens. This pulp is then thickened (4) tothe consistency required by the ink releasing process. The effluentsproduced by this thickening stage can easily be recycled, as they arecold and do not contain much fibers and very little ink. At thebeginning of the following ink-releasing step (5) chemicals are mixedtogether with the fiber suspension. Caustics are added in order to raisethe pH up to 9-10, together with oxydizing agent (such as hydrogenperoxide), and stabilizers (such as sodium silicate), and dispersingagents (surfactants, etc. . . ). The basic parameters of this process, -temperature, pressure, specific energy, chemicals dosing - will bedetermined in order to insure the optimum detachment of the inkparticles from the surface of the fibers together with their finestdispersion inside the pulp.

In the following examples, this operation has been made in a kneader,also called triturator, which permits the temperature to be brought tothe desired value (i.e. above the melting point of the ink vehicles)within few seconds and simultaneously applies very strong shear forcesat high consistency and in presence of de-inking agents.

The principle of the operation is that at first, the combined actions ofink-releasing chemicals and temperature (90°-130° C.) will soften theink vehicles and weaken the bondings between the same and the fibers,and then the combined actions of ink-dispersing chemicals and intenseshear forces will detach and finely disperse these particles inside thefiber suspension. The high consistency (20-30%) allows to treat very lowvolumes of pulp in small machines during a very short time (2-3minutes), .Iadd.for example 1 to 5 minutes or 2 to 10 minutes,.Iaddend.thus avoiding the yellowing of the pulp and increasing theefficiency of the chemicals.

This pulp then remains 5 to 20 minutes in a latency chest (6), at aconsistency between 2% and 5%. It may then be deflaked (7) in order tothoroughly separate the fibers bundles one from the other, and thusfacilitate the ink removal from the slurry.

The fibrous suspension finally goes through the ink removal process (8)which can be advantageously composed of multi-stage, counter-current,high consistency washing. The number of stages is choosen according tothe quantity of ink to be removed and to the desired final brightness.The extraction of the water is conducted through strains of perforatedplates, the dimensions of the openings of which will be selected inorder to allow for a given quantity of fibers to be carried awaytogether with the effluent, thus ensuring the optimum operation of boththe following ink selective separation process, and the final filtrationof the recovered satellite secondary pulp.

In case a filler-free secondary pulp is desired, the effluents from thewashing step (8) can advantageously be strained again on one or severalfine mesh filters (9). By this means, it is possible to remove at eachfilter stage up to 80% of the mineral fillers contained in that slurry.In such a case, the finest fraction must be sent to a conventionalalkaline clarifier (10) and then be disposed of. The clarified fractionis then returned ahead or after the following ink selective separationstep (11), according to the operating parameters of this last process(consistency, temperature), and according to the required brightness.

The necessary chemicals are also introduced ahead of this step. In casethis process is a selective flotation, ink collectors such as fattyacids or their sodium or calcium soaps can be added, taking care toinsure a mixing time of about 5 minutes at a temperature of about 35° to45° C.

It may be worthy to recall that the dispersing agent used during thewashing step has a negative effect both on the coagulation produced bythe collecting agents during the flotation step, and on the drainability(freeness) of the fibrous suspension during the filtration step. It willbe good to inactivate or neutralize these agents for example byprecipitation with calcium chloride or calcium hydroxide. Theprecipitation of the sodium silicate will also contribute to increasethe brightness of the secondary pulp through the formation of aprecipitated mineral filler. It has also been observed that the quantityof mineral fillers removed together with the foam during the flotationstep may vary from 30% up to 70% according to the operating parametersof the process: flotation time, temperature, pulp consistency, dosingand type of chemicals. The rejected foam containing the ink is thenpumped to centrifuges or filter-presses and disposed of. The loss ofsolid particles has been observed to be between 10% and 20% of the flowof secondary pulp, which means about 3% to 6% of the total quantity ofpulp feeding the washing step (8).

It has also been observed that the maximum efficiency of the ink removalhas been reached at much higher consistencies that the ones recommendedby the suppliers of the cells. For example, a cell designed to work at1% has shown best results between 1,5% and 2%. This peculiarity allowsfor the treatment of lowest quantities of effluents, using higherconsistencies during washing, and larger holes in the extractorsperforated plates.

When the requested concentration for the ink selective separationprocess is higher (say 0,5% or more) than the maximum concentrationwhich can be given to the effluent of the washing step, some heavy stockcan be advantageously extracted from the latency chest (6). In thiscase, the small quantity of long fibers added to the secondary pulp willhelp in forming the filtering mat in the final filtration step (12).

The selective separation of the ink (11) can also be a process based onadsorption of the ink upon the surface of non-soap solids, asrecommended by Ira Puddington et Al. in the U.S. Pat. No. 4,076,578.

The de-inked slurry leaving the process (11) is then filtered on fibrousmat up to at least 4% consistency, possibly above 10% in order to removefrom the final secondary pulp the maximum possible quantity of dissolvedsalts.

In case this pulp contains a very high quantity of ground-wood fines andfillers (such as mixtures of newsprint and magazine paper), the pH aheadof the filtration step has to be dropped down to values below 8, byaddition of sulfuric acid (preferably to aluminum sulfate), underintense mechanical agitation (as could be the suction side of acentrifugal pump), and after some long fibers extracted from the washedfinal primary pulp has been added to the the satellite slurry to befiltered.

It has been observed that the application of equipment such as Polydiskor Waco Filters to the thickening process (12) has permitted to produceclear filtrate having less that 100 ppm suspended solids andconsequently totally re-usable in the pulping (2), cleaning (3) andwashing (8) processes without any further clarification.

The final thickened secondary pulp leaving (12) must then be brought toa pH compatible with the following use by addition of sulfuric acid oraluminum sulfate, always under intense mechanical agitation, and can bestored in a buffer chest according to the final use.

EXAMPLES

The following examples will illustrate three different applications ofthe general procedure previously described, using different mixtures ofwaste paper and producing different grades of paper and board.Measurements of brightness were made with an Elrepho meter with 457 mm.light filter, according to I.S.O. standards. Chemicals dosings areexpressed in percent by weight of the chemical at 100% concentrationrelative to the weight of total solids in the line where said chemicalis added. Sodium silicate is considered at 38° Be and the Removink F andL as supplied.

EXAMPLE 1

The raw material is a mixture of over-issued newspapers and telephonebooks (white and yellow pages) in a ratio approximately 50/50. Thede-inked pulps are used for the production of newsprint and telephonedirectory papers (white and yellow), on only one high speed papermachine.

In this installation, the pulper has a capacity of 46 m³ containing2.700 kg of waste paper. Each batch takes 30 min. Dilution water iscoming from the effluent of the thickening process (4) and make-up ismade using clear filtrate from the Polydisk filter (12). One percent ofsodium hydroxide is added in the pulper together with 1% of a de-inkingagent such as Removink L 8001 supplied by Chemicarta SPA, Milano..Iadd.This pulping step typically is performed at ambient or roomtemperature. .Iaddend.When this cold pulping operation is finished, thestock is pumped through turboseparator, screens and cleaners, atconsistencies starting around 4% and ending at about 0,6%.

The turboseparator is equipped with a perforated plate having 3 mm.diameter holes and the rejected stock is then sent to a vibrating flatscreen also having 3 mm. holes, the rejects of which are disposed of.

The accepted stock from the turboseparator is then diluted from 3% downto 1% before it passes through pressurized slotted screens fitted with0,30 mm. slot width. The rejected stock is processed through a secondstage screen having the same slot size, and rejects of the same go to avibrating flat screen, rejects of which are disposed of.

The accepted stock from the first stage of screens is then diluted downto 0,6% consistency and processed through a conventional battery of 4stages of Triclean cleaners. The light and the heavy rejects of the 4thstage are disposed of.

The total loss of both high and low consistency turboseparating,screening and cleaning is varies between 6% and 9% by weight, dependingupon the

degree of contamination of the waste paper.

No more stickies or hot melts can be seen in the pulp, and a visualinspection is confirmed by the Sommerville test, which shows less than0,2% of shives. At that point, the pulp is totally cleaned and the onlyremaining contaminant is the printing ink. The pulp is then thickened upto 30% consistency in two steps, using a disk filter up to 10-12% andthen a screw press up to 30%. Characteristics of the pulp are:brightness=40°-45° ISO, freeness=50°-55° SR, filler content=6-8%,temperature=20°-25° C. The ink releasing step (5) is achieved in akneader under the following operating conditions: temperature=95°-98°C., sodium hydroxide=1,5% , sodium silicate=4% , hydrogen peroxide=1,8%, specific energy=80 KW.H/Ton during 3 minutes. The brightness of thepulp at the end of the treatment is 50°-55° ISO, and freeness is 60°-65°SR. The pulp is then diluted using all the flow of effluents coming fromthe second stage of washers, then squeezed up to 12% in the firstwashing stage.

These washers are composed of inclined screws (better known asRice-Barton or Baker's screws), where the pulp is drained undercontinuous and vigorous agitation through perforated plates having 1,4mm. diameter holes, in order to produce an effluent having approximately0,8-1% consistency.

The thickened stock is then processed through two other similar countercurrent washing steps and the final usable pulp presents the followingcharacteristics: brightness=59°-60° ISO, freeness=46°-50° SR, fillercontent 2-3%, consistency=12-14%. This pulp represents 78% by weight ofthe quantity of pulp feeding the washers (8). The balance 22% is goingto the satellite circuit with the first stage effluent which showsbrightness=35°-40° ISO, filler content=20-25%, freeness=80° SR.

The capability for the ink of being removed from the fibers contained inthe effluent has beenverified in the laboratory as follows: an effluentsample has been hyperwashed under fresh water shower on a 200 mesh wire,and a handsheet has been made, showing a brightness of 56° ISO, whichis very similar to the brightness of the final primary pulp. Thiseffluent has then been mixed together with 4% of a specialink-collecting agent purposely designed for this application byChemicarta SPA, Milano, and kept for 5 min. under agitation at 30° C.

The mixture is then processed through one single stage conventionalflotation cell, Voith open type, during 15 min.. The loss of weightthrough the cell is 15-20%, which means only 3-4,5% respect to the totalquantity of pulp entering the washers. We have found that addition of0,5% to 1% of calcium chloride or calcium hydroxide together with thecollector, ahead of the flotation, helps controlling the foam and theink coagulation when low ash content pulps are processed.

The total alkalinity is then dropped down to pH=7-8 with addition of 1%of sulfuric acid on the suction side of the centrifugal pump feeding thedisk filter (12). At this point, the pulp shows a brightness=53°-56°ISO, a filler content=15-20% and a freeness=78°-80° SR.

The disk filter (12) is a Polydisk filter sized according to a specificfiltering factor=20 liters/min./m2. Besides this unusual value, it isalso necessary to feed the mat-peeling showers with air instead ofwater, in order to reach the maximum possible consistency of thedischarged pulp.

Using the above mentioned parameters, a final consistency of 8% to 10%could be obtained and the clear filtrate shown less than 100 ppm averagesuspended solids, measured on paper filter, black label.

The pulp is then brought to pH=6 and sent to a buffer chest having 8hours total retention time. From this point, it is then pumped to themixing chest of the paper machine at controlled flow rates according tothe paper grade actually produced and in function of the meancomposition of the secondary pulp.

The clear filtrate from the Polydisk filter is then totally recycled inorder to dilute the stock ahead of the third washing stage and make-upis provided by fresh industrial water which does not contain aluminiumions.

The application of such a process in a paper mill having one singlepaper machine offers the following advantages:

(a) possibility to maintain constant freeness and ash content during agrade run, independently from the incoming waste paper characteristics,thus allowing the paper machine to run at maximum speed and efficiency;

(b) possibility to achieve very quick grade change, exactly as whenusingvirgin pulp and fillers, without the need to intervene a long timebefore in the waste paper plant, thus permitting an easier and moreconstant operation of that plant;

(c) possibility to always use the highest possible quantity of recycledfibers in the paper, by the free disposal of each one of the twofractions and their use in the optimum way.

(d) possibility to produce totally cleaned pulps having the samestandards of cleanliness than virgin pulps and thus offering the highestpossible runability in the paper machine room, particularly being freeof any "sticky" or "hot melt" or ink vehicle free particle.

EXAMPLE 2

The raw material is a mixture of printed continuous stationary , oldbooks and office file, in a ratio 50/50.

The de-inked pulp is used to produce, on three distinct paper machines:(a) light weight machine-glazed wrapping papers, (b) fine papers forwriting and printing, including wood containing printing grades, (c)stationary and continuous print-out papers.

The operation is similar to example (1) up to the thickening step (4),although it is not necessary to add any chemical agent--caustics orde-inking agent--during the pulping step (2). When entering theink-releasing step (5), the pulp has a brightness=60° ISO, afreeness=40°-45° SR, and a filler content=20%.

The ink-releasing equipment is the same as for example (1) but operatingparameters are as follow: Removink L8001=0,3%; hydrogen peroxyde=0,5%,sodium hydroxyde=1%, sodium silicate=3%. All other parameters remainunchanged. At the end of the process, the pulp has shown a brightnessincrease of 2° ISO and freeness did not show any appreciable variation.

The pulp is then washed by mean of three washing stages as for example(1), but the design of the perforated plates are different: the firststage is fitted with 2 mm. diameters holes, the second and the thirdstages are equipped with 1,4mm. diameter holes. Also the feedconsistency of the washing stages is different, being 2,5%. With theseparameters, the final washed primary pulp has shown followingcharacteristics: brightness=75° ISO, filler content below 3%, freeness27°-30° SR.

The effluent leaving the first washers has a consistency between 1% and1,2%, a filler content=60%, brightness=50° ISO, and freeness=70° SR.

The flotation cell used in this application is a high consistency Swemactype, and heavy stock has been pumped from chest (6) and mixed togetherwith the effluent before the flotation, in order to raise theconsistency up to 1,5%. In this way, the two lines (primary by washingand secondary by flotation) have exactly the same solids flow rate, orthe same capacity in tons/day, but produce two pulps having oppositecharacteristics. This extraction also procures long fibers which willhelp the final filtration (12).

This extraction could have been done using washed pulp and this wouldhave increased the brightness of the secondary pulp. But in such a case,the washing equipment would have to be sized for 30% more capacity,which is not a worthy choice in our case.

The flotation is then conducted with only 2% of the same collector(Removink F) and the retention time through the cell is only 10 min.,thus producing a loss of weight of 10% (which means 5% of the totalpulp).

After acidification at pH=8 ahead of the disk filter, the pulp shows abrightness=70° ISO, a filler content=35-40%, a freeness=65°-70° SR.

The Polydisk filter can be sized using a filtering factor=25liters/min./m2, and produces an effluent containing 70-100 ppm suspendedsolids. The other steps of this application are similar to the onesdescribed in example (1).

The application of such a process in a paper mill having several papermachines as in this example is offering the following advantages:

(a) possibility to produce a pulp having physical and cleanlinesscharacteristics similar to the ones of a virgin chemical pulp, thususable for the production of fine light weight papers, with good Yankeedryer glazing capabilities;

(b) possibility to produce a pulp having physical and opticalcharacteristics of a mixture of fine chemical and/or ground-wood pulp,and mineral fillers, thus usable for the production of printing paperswhere high opacity and smoothness are requested.

(c) possibility to mix these two pulps together in a ratio which can bevery much different from the original one coming together with the rawmaterial.

EXAMPLE 3

The raw material is a mixture of low quality printed waste, containingold books, office waste and stationary, and some newspapers andmagazines, in variables proportions.

The mill has one multiply board machine, and produces high qualityfolding box board, which can be on-machine coated and must show anexcellent multicolour offset printing aptitude. The white top liner iscomposed of 100% de-inked primary pulp and the underliner uses thesecondary pulp, mixed with other pulp.

Pulping is conducted in a continuous way with the same parameters as forexample 1. The cleaning and screening treatment (3) is simplified andcomposed of centrifugal high-density cleaners, followed by aturboseparator, working at 3% consistency. The following thickeningstage is also simplified and composed of inclined screws producing pulpat 15% consistency, followed by a screw press. The finest contaminantswill be detached and better dispersed during the ink-releasing step (5)and then carried away with the effluent during the washing stage. Theywill remain in the secondary pulp thus contributing to add weight andvolume to the board, as the underliner does not need to be particularlycleaned.

The pulp entering the ink-releasing and dispersing step shows abrightness=50° ISO, a filler content=25-30%. The operating parametersare the same as for example (1), but the brightness drops down to46°-48° ISO.

The following washing step has only two stages, which are fed at 2,5%consistency. The perforated plates of the inclined screws have 1,6 mm.diameter holes, and it has been found that the characteristics of theeffluent are very similar to the one of example 1.

The washed primary pulp shows a brightness=68° ISO, a filler content=4%and a freeness=45°-50° SR. The fine cleaning of the primary pulp isachieved with the cleaners and the screens installed ahead of the boardmachine, which is sufficient to reach the desired quality. It must besaid that the contaminants have been thoroughly dispersed in the kneader(5) and most of them have left this primary pulp during the washingstep.

The satellite circuit is also simplified because the brightness of theunderliner has only a third-order influence on the final brightness ofthe coated board. We have observed that a brightness of the underlinersecondary pulp in the 50° ISO range was sufficient to insure therequired brightness 80° ISO of the coated board, providing that the topliner primary pulp has 70° ISO. Thus, the flotation time has beenreduced below 10 min. and the dosing of the collector has been keptbelow 2%. We have also observed that it was possible to run without anychemical when lower quality grades are produced, but no compromise canbe applied on the dispersion effect, because black spots in theunderliner are always visible even through the coated top liner.

The application of such a process to the production of stratified boardis offering the following advantages:

(a) possibility to totally replace chemical pulp or high qualityselected unprinted waste paper by a low value and large availability rawmaterial;

(b) simplification of the main line by eliminating the fine screeningand cleaning equipment;

(c) increase of the total yield, by transferring in the secondary pulp(and then in the underliner or in the middle ply) all finely dispersedcontaminants which are not acceptable in the top liner.

I claim:
 1. A method of treating a mixture of printed and contaminatedwaste paper in order to produce a pulp for use in the manufacture ofpaper and paperboards, said waste paper containing non-ink contaminantsincluding stickies, which method comprises:(a) forming a first aqueousfibrous suspension of said waste paper at room temperature by applyingspecific mechanical energy lower that 50 KW.H/Ton to form a pumpableslurry and to release substantially all of the non-ink contaminantsincluding the stickies, from the surface of the paper and withoutdispersing such non-ink contaminants as finely divided particlesthroughout the fibrous suspension; (b) removing substantially all of thenon-ink contaminants including the stickies, which have been releasedwithout dispersal as finely divided particles from the first fibroussuspension by screening and cleaning at room temperature to form asecond aqueous fibrous suspension substantially free of the non-inkcontaminants including the stickies; (c) after the step of removing thenon-ink contaminants softening the ink vehicles and weakening theirbinding with the surface of the fibers by submitting the second fibroussuspension at a consistency of more than 15% to the simultaneous actionsof (A) a high temperature between 85° and 130° C., (B) high shear forcessubstantially corresponding to a specific mechanical energy of more than50 KW.H/Ton applied at the said consistency of more than 15% and (C) atleast one deinking agent under strong alkaline conditions having a pH ofat least 9; and (d) detaching the ink particles from the surface of thefibers and dispersing them into the second fibrous suspension bysubmitting the second fibrous suspension to the simultaneous actions of(A) high temperature between 85° and 130° C., (B) high shear forcessubstantially corresponding to a specific mechanical energy of more than50 KW.H/Ton applied at the said consistency of more that 15% and (C) atleast one chemical dispersing agent, under strong alkaline conditionshaving a pH of at least 9 whereby higher specific energy inputs andhigher temperatures are used to detach the ink particles from the fibersof the second fibrous suspension after removal of the non-inkcontaminants than are used on the first fibrous suspension beforeremoval of the non-ink contaminants; (e) limiting the total duration ofthe ink softening and detaching steps (c) and (d) to a range between 2and 10 minutes and (f) removing the detached ink particles from thesecond fibrous suspension to provide a brightness of at least 59 ISO thefinal pulp.
 2. The method of claim 1 wherein the specific energy appliedto the fibrous suspension during the forming step (a) is applied forapproximately 20 minutes.
 3. The method of claim 1 wherein the inksoftening and detaching steps (c) and (d) are conducted at a pressurehigher than the atmospheric pressure.
 4. The method of claim 1 whereinthe total duration of the ink softening and detaching steps (c) and (d)is kept between 3 and 5 minutes.
 5. The method of claim 1 wherein thetotal specific energy applied during the ink softening and detachingsteps (c) and (d) is about 80 KW.H/Ton.
 6. The method of claim 1 whereinthe ink softening and detaching steps (c) and (d) are performedsimultaneously in a single apparatus.
 7. The method of claim 1 whereinthe ink softening and detaching steps (c) and (d) are performedseparately in two different pieces of equipment.
 8. The method of claim1 wherein the removing of the ink particles from the fibrous suspensionis achieved by washing.
 9. The method of claim 1 wherein the alkalinityof the fibrous suspension in steps (c) and (d) is obtained by adding anyone of the following chemicals:sodium hydroxide, potassium hydroxide,calcium hydroxide, magnesium hydroxide, sodium carbonate, sodiumphosphate, sodium tripolyphosphate, sodium pyrophosphate, sodiumsilicate.
 10. The method of claim 1 wherein an oxidizing agent is addedduring the ink softening and detaching steps (c) and (d).
 11. The methodof claim 1 wherein a bleaching action is performed during the inksoftening and detaching steps (c) and (d).
 12. The method of claim 1wherein the ink softening and detaching steps (c) and (d) are performedsimultaneously in a triturator.
 13. The method of claim 1 wherein theink softening and detaching steps (c) and (d) are performedsimultaneously in a disintegrator.
 14. A method of claim 1 wherein theink softening and detaching steps (c) and (d) are performed separatelyin a steaming chamber followed by a disperser.
 15. The method of claim 1wherein the step of removing the ink particles from the fibroussuspension is achieved by froth flotation.
 16. The method of claim 1wherein the step of removing the ink particles from the fibroussuspension is achieved by washing and froth flotation.
 17. The method ofclaim 1 wherein the alkalinity of the fibrous suspension in steps (c)and (d) is obtained by adding a mixture of chemicals selected from thegroup consisting of, sodium hydroxide, potassium hydroxide, calciumhydroxide, magnesium hydroxide, sodium carbonate, sodium phosphate,sodium tripolyphosphate, sodium pyrophosphate, sodium silicate.
 18. Themethod of claim 1 wherein the ink softening and detaching steps (c) and(d) are achieved at a consistency between 25% and 30%. .Iadd.
 19. Amethod of treating a mixture of printed and contaminated waste paper inorder to produce a pulp for use in the manufacture of paper andpaperboards, said waste paper containing non-ink contaminants includingstickies, which method comprises:(a) forming a first aqueous fibroussuspension of said waste paper at ambient temperature by applyingspecific mechanical energy lower than 50 KW.H/Ton to form a pumpableslurry and to release substantially all of the non-ink contaminantsincluding the stickies, from the surface of the paper and withoutdispersing such non-ink contaminants as finely divided particlesthroughout the fibrous suspension; (b) removing substantially all of thenon-ink contaminants including the stickies, which have been releasedwithout dispersal as finely divided particles from the first fibroussuspension by screening and cleaning at ambient temperature to form asecond aqueous fibrous suspension substantially free of the non-inkcontaminants including the stickies; (c) after the step of removing thenon-ink contaminants, softening the ink vehicles and weakening theirbinding with the surface of the fibers by submitting the second fibroussuspension at a consistency of more than 15% to the simultaneous actionsof (A) a high temperature between 85° and 130° C., (B) high shear forcessubstantially corresponding to a specific mechanical energy of more then50 KW.H/Ton applied at the said consistency of more than 15% and (C) atleast one deinking agent under strong alkaline conditions having a pH ofat least 9; (d) detaching the ink particles from the surface of thefibers and dispersing them into the second fibrous suspension bysubmitting the second fibrous suspension to the simultaneous actions of(A) high temperature between 85° and 130° C., (B) high shear forcessubstantially corresponding to a specific mechanical energy of more than50 KW.H/Ton applied at the said consistency of more than 15% and (C) atleast one chemical dispersing agent, under strong alkaline conditionshaving a pH of at least 9 whereby higher specific energy inputs andhigher temperatures are used to detach the ink particles from the fibersof the second fibrous suspension after removal of the non-inkcontaminants than are used on the first fibrous suspension beforeremoval of the non-ink contaminants; (e) limiting the total duration ofthe ink softening and detaching steps (c) and (d) to a range betweenabout 1 and 5 minutes; and (f) removing the detached ink particles fromthe second fibrous suspension to provide a brightness of at least 59 ISOto the final pulp..Iaddend..Iadd.20. A method of treating a mixture ofprinted and contaminated waste paper in order to produce a pulp for usein the manufacture of paper and paperboards, said waste paper containingnon-ink contaminants including stickies, which method comprises: (a)forming a first aqueous fibrous suspension of said waste paper at a lowtemperature by applying specific mechanical energy lower than 50KW.H/Ton to form a pumpable slurry and to release substantially all ofthe non-ink contaminants including the stickies, from the surface of thepaper and without dispersing such non-ink contaminants as finely dividedparticles throughout the fibrous suspension, the low temperature beingsufficiently low to maintain rigidity of non-ink contaminants having alowest melting point so that the lowest melting point non-inkcontaminants will not extrude through screens; (b) removingsubstantially all of the non-ink contaminants including the stickies,which have been released without dispersal as finely divided particlesfrom the first fibrous suspension by screening and cleaning at the lowtemperature to form a second aqueous fibrous suspension substantiallyfree of the non-ink contaminants including the stickies; (c) after thestep of removing the non-ink contaminants softening the ink vehicles andweakening their binding with the surface of the fibers by submitting thesecond fibrous suspension at a consistency of more than 15% to thesimultaneous actions of (A) a high temperature between 85° and 130° C.,(B) high shear forces substantially corresponding to a specificmechanical energy of more than 50 KW.H/Ton applied at the saidconsistency of more than 15% and (C) at least one deinking agent understrong alkaline conditions having a pH of at least 9; (d) detaching theink particles from the surface of the fibers and dispersing them intothe second fibrous suspension by submitting the second fibroussuspension to the simultaneous actions of (A) high temperature between85° and 130° C., (B) high shear forces substantially corresponding to aspecific mechanical energy of more than 50 KW.H/Ton applied at the saidconsistency of more than 15% and (C) at least one chemical dispersingagent, under strong alkaline conditions having a pH of at least 9whereby higher specific energy inputs and higher temperature are used todetach the ink particles from the fibers of the second fibroussuspension after removal of the non-ink contaminants than are used onthe first fibrous suspension before removal of the non-ink contaminants;(e) limiting the total duration of the ink softening and detaching steps(c) and (d) to a range between about 1 and 5 minutes; and (f) removingthe detached ink particles from the second fibrous suspension to providea brightness of at least 59 ISO to the final pulp..Iaddend..Iadd.21. Amethod of treating a mixture of printed and contaminated waste paper inorder to produce a pulp for use in the manufacture of paper andpaperboards, said waste paper containing non-ink contaminants includingstickies, which method comprises:(a) forming a first aqueous fibroussuspension of said waste paper at a low temperature by applying specificmechanical energy lower than 50 KW.H/Ton to form a pumpable slurry andto release substantially all of the non-ink contaminants including thestickies, from the surface of the paper and without dispersing suchnon-ink contaminants as finely divided particles throughout the fibroussuspension, the low temperature being sufficiently low to maintainrigidity of non-ink contaminants having a lowest melting point so thatthe lowest melting point non-ink contaminants will not extrude throughscreens; (b) removing substantially all of the non-ink contaminantsincluding the stickies, which have been released without dispersal asfinely divided particles from the first fibrous suspension by screeningand cleaning at the low temperature to form a second aqueous fibroussuspension substantially free of the non-ink contaminants including thestickies; (c) after the step of removing the non-ink contaminantssoftening the ink vehicles and weakening their binding with the surfaceof the fibers by submitting the second fibrous suspension at aconsistency of more than 15% to the simultaneous actions of (A) a hightemperature between 85° and 130° C., (B) high shear forces substantiallycorresponding to a specific mechanical energy of more than 50 KW.H/Tonapplied at the said consistency of more than 15% and (C) at least onedeinking agent under strong alkaline conditions having a pH of at least9; (d) detaching the ink particles from the surface of the fibers anddispersing them into the second fibrous suspension by submitting thesecond fibrous suspension to the simultaneous actions of (A) hightemperature between 85° and 130° C., (B) high shear forces substantiallycorresponding to a specific mechanical energy of more than 50 KW.H/Tonapplied at the said consistency of more than 15% And (C) at least onechemical dispersing agent, under strong alkaline conditions having a pHof at least 9 whereby higher specific energy inputs and highertemperature are used to detach the ink particles from the fibers of thesecond fibrous suspension after removal of the non-ink contaminants thanare used on the first fibrous suspension before removal of the non-inkcontaminants; (e) limiting the total duration of the ink softening anddetaching steps (c) and (d) to a range between 2 and 10 minutes; and (f)removing the detached ink particles from the second fibrous suspensionto provide a brightness of at least 59 ISO to the final pulp..Iaddend.